Calibration method of spectroradiometer based on direct solar irradiance

Optical design and spectral calibration of the visible-near infrared irradiance monitor

“…where λ represents the incident wavelength, f indicates the focal length of the prism, a denotes the slit width, x 0 stands for the size of the zero-order diffraction spot, θ 1 is the divergence angle of the Sun (approximately 0.5 deg), and γ indicates the incident angle. 22 The meanings of these symbols are described in Figs. 4 and 8.…”

“…Before working outdoors, the VISM is calibrated and tested in the laboratory to ensure compliance with the design requirements, which mainly includes spectral calibration and radiometric calibration. 22 Through the spectral calibration of VISM, it is known that the pixel number of the CCD corresponds to the wavelength at which the sunlight enters the photodiodes of the main optical path. In the traditional way of spectral calibration, there are a lot of characteristic spectra emitted by the lamps or monochromators as required.…”

“…( 2) In the near-infrared, there are few characteristic spectra available, and their energy is quite limited, which leads to the low accuracy of spectral calibration. 22 In this paper, a novel method of spectral calibration is developed. Based on the optical layout of the VISM and the dispersion equation of the prism, this new method is implemented in three steps.…”

“…There are two methods applicable to assess uncertainty: type A and type B. 22 The evaluation of type A relies on statistical analysis of the measurement results, whereas the evaluation of type B is reliant on the empirical data or calibration results obtained from authoritative institutions. Because the uncertainty of the spectral calibration for VISM primarily relies on partial measurement data and calibrated certificates, the evaluation of type B is performed in this paper.…”

“…where U represents the combined uncertainty and U 1 to U m represent the uncertainty caused by different factors. 22 3.3 Outdoor Observation of the VISM When the VISM completes the spectral calibration and radiometric calibration, VISM can be placed outdoor to determine the solar spectral irradiance. The method of radiometric calibration for VISM will be discussed in a separate paper.…”